With the development of the society and the improvement of the living standard, people are taking more requirements on the comfort, safety and stability of vehicle riding. As an important part of modern car, the performance of suspension system has great influence on riding comfort and operating stability. Hence, the researches on active suspension system are drawn much more attention. As the core component of the active suspension system, the researches on tubular motor have been paid more attention.
Domestic and foreign scholars have proposed many different tubular motor topologies, which are suitable for different fields. Tubular motor can be divided into different types with different classification standards. It can be divided into long-stator and long-mover tubular motor according to the different length between the stator and the mover. It can be divided into the primary PM and secondary PM tubular motor according to the different position of PMs. Also, It can be divided into single-stator and dual-stator tubular motor according to the different number of stator. The Chinese Invention Patents CN 101882819 A and CN 101795048 B show a primary and secondary tubular permanent-magnet (TPM) motor, respectively. It can be noticed that the primary PM motor greatly increased the amount of PMs, while the secondary PM tubular motor increased the length of the armature. These all greatly increase the cost of design and production, and seriously hinder the application and promotion of tubular motor. Compared with dual-stator TPM motor, the single-stator TPM motor has simple structure, and can be easy to produce, thus has lower cost of design and production. In addition, the low loss and easy heat dissipation of the single-stator TPM motor are also the main reasons for its wide using. However, dual-stator tubular motor has become a research hotspot with the advantages of high mechanical integration, high space utilization, high thrust density and low thrust force fluctuation.
In addition, the switch-flux TPM linear synchronous motor can be used to decrease the cost caused by the long armature and magnetic pole structure. Because PMs are sandwiched by armatures, which are placed on the stator or the mover, so the amount of PM and cost is great decreased. However, new problems are produced: the heat dissipation condition is too bad due to the PMs being enclosed by the armatures, the motor temperature rises seriously; the slot area and PM position interact with each other, thus the thrust force density is limited severely and the efficiency of motor is decreased.
When the fault-tolerant motor is with one or two short-circuit phase faults, the motor still has a capability of output certain thrust force or torque. However, the thrust force or torque is seriously distorted, and the noise is also increased greatly, which seriously affect the system performance. The FTC goal is to optimize the fault-tolerant current for different applications, and then the output thrust force or torque can be as smooth as possible under the fault condition. And furthermore, the faulty motor performance can reaches or approaches that in the healthy condition. The Chinese invention patent 201510059387.2 is “A short-circuit fault-tolerant control method for five-phase fault-tolerant permanent-magnet motor”. The five-phase surface mounted PM rotating motor was with short-circuit phase fault. The impact of short-circuit fault on motor torque is decomposed into two parts: one is the impact of open-circuit fault on torque; the other is the influence of short-circuit current on torque. By using the principle of the constant magneto-motive forces (MMFs) both in pre- and pro-fault conditions and the constraint of the equal amplitudes of the remaining healthy phase currents, the remaining healthy phase currents were optimized under the open-circuit fault condition. To restrain the torque fluctuations caused by the short-circuit current, the healthy phase compensatory currents were obtained according to the principle that MMFs was zero and copper loss was minimum under fault condition. Finally, the current references of the remained healthy phase were obtained by adding the two currents. According to the obtained remaining healthy phase currents, the current hysteresis control strategy was adopted to control the five-phase surface mounted PM rotating motor. In this method, the amplitude of the compensatory currents in the remaining healthy phases is constant, which used to suppress the torque fluctuations caused by short-circuit currents. The amplitude of the compensatory currents has no relation to the motor speed, and the sum of the compensatory currents in the remaining healthy phases is not zero. Meanwhile, this method is not suitable for fault-tolerant operation in double-phase faults (open-circuit, short-circuit or one phase open-circuit and another phase short-circuit). Currently, the common FTC method is always to calculate the fault-tolerant currents and then to use the current hysteresis control strategy. However, this method has problems such as: disordered switching frequency, large noise, and poor dynamic performance. Hence, it is not suitable for applications of high power and strict requirements on dynamic performance. The Chinese invention patent 201510661212.9 is “A short-circuit fault-tolerant field-oriented control method of interior hybrid magnetic material fault-tolerant tubular linear motor”. It is aimed that five-phase hybrid magnetic material interior fault-tolerant linear motor under one short-circuit phase faults. The aforementioned method was used to optimize the remaining healthy currents, then the field-oriented control strategy was used to realize the field-oriented control operation under one short-circuit phase fault. Although high fault-tolerant performance, high dynamic performance, and good current tracking ability are achieved under short-circuit phase fault condition, this method cannot achieve field-oriented control under double-phase fault condition (open-circuit, short-circuit, or one phase open-circuit and another phase short-circuit).